Chlorination of propylene dichloride



y 1938. A. A. LEVINE ET AL 2,119,484

CHLORINATION OF PROPYLENE DICHLORIDE Filed May 6, 1935 BOILING POINT OF PROPYLENE DICHLORIDE O AT ATMOSPHERIC PRESSURE qv c IRON A CATALYST 6O IRON ULTRA VIoLET LIGHT s cATALYsT DEGREES CENTIGRADE 010 4o 6O so qo Ioo I, 2,; CHLOROPRODANE Ioo Q0 50 7O 6O 50 4o 30 2o 10 0 v0 I, I,& CHLOROPROPANE IN VEN TORS ARTHUR A. LEVINE BY OLIVER W. CA-ss A T'TORNEY Patented May 31, 1938 2,119,484 CHLORINATION OF PROP'YLENE DICHLO- BIDE Arthur A. Levine and Falls, N. Y., assignors Oliver W. Cass, Niagara to E. I. du Pont de Nemours & Company, Wilmington, DeL, a corporation of Delaware Application May 6, 1935, Serial No. 19,954

12 Claims.

This application relates to the halogenation of organic compounds and more particularly to the chlorination of such compounds. Specifically, the process disclosed in this application is concerned with the chlorination of propylene dichloride under conditions which permit the resulting products to be selected and the relative amount thereof regulated.

Propylene dichloride or dichlorpropane CI-LaCHCLCHzCl, is conveniently prepared by chlorinating propylene, CHaCHtCI-Ia. In this process a chlorination catalyst such as iron, ferric chloride, aluminum chloride, iodine, or sulfur may be used. The addition of chlorine to the propylene takes place directly in the cold when chlorine in the gaseous state is brought into contact with the hydrocarbon in the presence of a mutual solvent such as propylene dichloride. The product as formed is continuously withdrawn.

Propylene dichloride, when pure, is a colorless liquid having a boiling point of about 97 C. Ordinarily when it is chlorinated, many products are present in the mixture remaining. Of these we are particularly interested in two trichlorpropanes. One of these isomers is the compound 1,l,2-trichlorpropane, CHClzCHCLCHa. The other isomer is 1,2,3 trichlorpropane, CHzCLCI-ICLCHCI. Both of these isomers are liquids having relatively high boiling points higher than that of the propylene dichloride. It is one of the objects of this invention to chlorinate propylene dichloride under conditions so selected and controlled that the yields of either of these isomers in the mixed product resulting may be made to predominate. Specifically, by following the process herein disclosed it is possible to control the relative porportions of the two isomers in the resulting product within relatively wide limits so that any specific ratio of the 1,2,3-trlchlorpropane to the 1,1,2-trichlorpropane as desired may be obtained.

Accordingly, the primary object of this invention is the development of a process for the chlorination of propylene dichloride so that the character of the resulting product may be controlled. It is another object of this invention so to carry out the chlorination that it is rapid and substantially quantitative in yield. Moreover another object is to provide a process by which propylene dichloride may be readily chlorinated in a relatively short period of time and without the necessity of maintaining unusually elevated temperatures or very low temperatures. Still another object of this invention is to control the yield of the two isomers referred to by the proper selection of the chlorination conditions so that the yield of either one of the two trichlorpropane isomers may be caused to predominate. Thus, if 1,1,2-trichlorpropane is the product desired, the amount of the 1,2,3 compound formed may be reduced to a very small proportion of the entire yield. Similarly if the 1,2,3 compound is valued most highly or is intended for use in some subsequent process, the quantity of the 1,1,2 compound resulting may be greatly reduced so that it is but a relatively negligible amount by the proper selection of the conditions of the halogenation. Another possible isomeric product, 1, 2, 2, trichlorpropane, is not produced to any appreciable amount by our method.

We have found that the chlorination of propylene dichloride may be carried out most effectively by using metallic iron as a catalyst. We have also found that iron and ultra-violet light together constitute a most eflicient catalyst. In our process the propylene dichloride is chlorinated directly in the liquid phase by the passage of gaseous chlorine into the vessel which contains the compound.

We have found that by selecting as a catalyst either metallic iron alone or metallic iron in coniunction with ultra-violet light it is possible to control the relative amounts of the trichlorpropane isomers resulting. Thus if a yield predominantly of the 1,2,3-trich1orpropane isomer is desired, we have found it most desirable to utilize a catalyst comprising iron and ultraviolet light in conjunction. On the other hand, if the 1,1,2-trichlorpropane product is the one most desired, metallic iron alone is our preferred catalyst.

Moreover it has been found that by selecting the catalyst used and also controlling the temperature at which the chlorination is carried out, it is possible to regulate the relative amounts of 1,1,2-trichlorpropane and 1,2,3-trichlorpropane in the reaction mixture. Since the process is a liquid phase reaction it is, of course, necessary that any temperature selected be below the boiling point of propylene dichloride. As previously stated, this compound boils at about 97 C. at atmospheric pressure. If desired. tooperate at a higher temperature, pressure may be applied thereby raising the boiling point of the compound. Ordinarily 97 C. represents the upper limit of the temperatures which we choose to employ in the chlorination herein disclosed. Similarly for commercial manufacturing operations it is normally not feasible to maintain a temperature much lower than -20 C. and for this reason this temperature must be regarded as a practical lower working temperature. The chlorination is therefore ordinarily carried out at some temperature between 20 C. and 97 C.and within this temperature range a choice of catalyst is made so that any desired proportion of the two trichlorpropane isomers will result in the reaction product.

The accompanying drawing illustrates the influence of temperature and the selection of the proper catalyst on the relative yields of 1,1.2-trichlorpropane and 1,2,3-trichlorpropane. As will be noticed, the drawing, which is a graph in which the relative yields of the isomers are plotted against the temperature, has plotted thereon curves in which the temperatures range from about 20 C. to 97 C. or above. As previously specified, this is our preferred working range. It will be noted that in both instances the plotted graphs are straight lines within these temperature limits.

The upper graph represents the conditions when iron alone is utilized as the catalyst. The lower graph is that corresponding to the use of iron and ultra-violet light conjointly as the catalyst. The figures at the bottom give not only the percentage yield of 1,1,2-trichlorpropane but also the percentage yield of 1,2,3-trichlorpropane for any point on the curves.

From these figures it is evident that by operating at approximately 18 C. with iron and ultra-violet light as the catalyst it is possible to obtain a yield consisting of about 90% 1,2,3-trichlorpropane. By operating at approximately 97 C., the boiling point of propylene dichloride, and using iron as a catalyst it is possible to obtain a yield which consists of approximately 86% 1,1,2-trichlorpropane. Thus if the predominance of either isomer in the reaction mixture is desired, these controlling conditions would be selected. For any other proportion of one isomer .tovthe other, other conditions intermediate between these two extremes are selected, utilizing the graphs as a guide.

If desired, it is possible to chlorinate the pro-' pylene dichloride under pressure so that a temperature in excess of 97 C. can be used while the reaction is still a liquid phase reaction. Thus by the application of pressure to a greater or less degree so that the pressure exceeds atmospheric, the propylene dichloride may be heated to' a temperature higher than 97 C. and still remain a liquid. Our invention is to be understood to include operating under increased pressure, the reaction remaining a liquid phase reaction, however. It is evident from the upper curve that by utilizing iron as a catalyst and a temperature of reaction in excess of 97 C. the yield of the 1,1,2- trichlorpropane isomer may be made to approach 100%.

But little need be said about the actual procedure involved in the chlorination process. Various details are given in the appended examples but the process may be readily carried out simply by bubbling chlorine gas into a vessel in which the propylene dichloride is contained. A stirrer has also been found to be practically essential in order to get efficient distribution of the chlorine throughout the liquid. The eiiluent hydrogen chloride which is one product of the reaction flows out from the reaction vessel and may be absorbed in water or some chemical absorbing medium such as caustic soda. The reaction product, being a liquid, remains in the vessel.

The separation of the isomers 1,2,3-trichlorpropane. and 1,1,2-trichlorpropane from each other and from any unreacted propylene dichloride remaining in the reaction mixture is readily column since there is a substantial difference in' their boiling points. As an example of our novel process the following may be given:

Example 1 2884 grams of propylene dichloride and 140 grams of iron filings ground to 40 mesh were placed in a 5 litre three-necked flask fitted with an inlet tube, a stirrer, and a reflux condenser leading to a scrubbing apparatus. The reaction vessel was maintained at a temperature ranging from 50-55 C. while a stream of chlorine gas was introduced through the gas inlet tube. Vigorous agitation was maintained by means of the stirrer.

326 grams of hydrogen chloride gas were evolved and absorbed in the medium in the scrubbing apparatus. The reaction mixture present in the flask was filtered to free it from metallic iron and then distilled in an eflicient column. After the unchlorinated propylene dichloride' had boiled off there were secured 506 gramsof 1,1,2- trichlorpropane, 474 grams of 1,2,3-trichlorpropane and grams of more highly chlorinated propancs. The trichlorpropane fraction. thus consists of 51.5% of 1,1,2-trichlorpropane and 48.5% of 1,2,3-trichlorpropane. The other trichlorpropane isomer 1,2,2-trichlorpropane, was practically entirely'absent.

As will be evident from the graph, the yield of 51.5% 1,1,2-trichlorpropane compares very favorably with the value for a temperature of about 51 C., as read from the upper straightline representing the conditions when iron alone is used as the catalyst.

Example 2 678 grams of propylene dichloride and 34 grams of iron filings ground to 40 mesh were placed in a 1 litre three-necked flask fitted with an inlet tube for chlorine, a stirrer, and a reflux condenser leading to a scrubbing system for the hydrogen chloride gas evolved. The reaction vessel was maintained at a temperature of 90 C.- C. by means of a water bath while a stream of chlorine gas was introduced with vigorous stirring. 108 grams of hydrogen chloride gas were evolved and the vapors passed on through the reflux condenser into the scrubbing liquid where they were absorbed.

The reaction mixture was then filtered to free it from metallic iron and'distilled through a 3 foot column filled with Raschig rings. After the unchlorinated propylene dichloride boiled ofl at about 97 C. there were secured 325 grams of 1,1,2-trichlorpropane, 44grams of 1,2,3-trichlorpropane and 45 grams of more highly chlorinated propanes. The other trichlorpropane isomer possible, 1,2,2-trichlorpropane, was practically absent in any substantial amount.

The trichlorpropane fraction thus consisted of 88.1% 1,1.2-trichlorpropane and 11.9% 1,2,3-trichlorpropane. It will be noted from the graph that this is very close to thevalues given for a temperature of about 95 C., on the upper curve, with iron alone as the catalytic agent.

Example 3 In this example a modified 5 litre flask fitted with a vertical Pyrex pletely through the flask was employed. It was provided with an inlet tube for chlorine, a stirrer, and a reflux condenser. In the flask 3000 grams of propylene dichloride and 45 grams of iron filings ground to 40 mesh were placed. A mercury arc lamp was then lowered through the Pyrex glass tube into the flask. The assembly was then cooled to a temperature or about 18 C.-15 C. by immersion in a bath of cooling medium.

Chlorine was then slowly admitted, with constant stirring, until some 400-500 grams had been added. The reaction mixture was filtered free of metallic iron and distilled through an efflcient column. After the unchlorinated propylene dichloride had been boiled away there was secured a product consisting of 52.3 grams of 1,1,2- trichlorpropane, 627 grams of 1,2,3-trichlorpropane and 132 grams of more highly chlorinated propanes.

The trichlorpropane fraction therefore consists of 92.3% of 1,2,3-trichlorpropane and 7.7% of 1,1,2-trichlorpropane while the other trichlorpropane isomer 1,2,2-trichlorpropane was practically absent. It will be noted that this value of 92.3% compares very favorably with the value given on the lower curve in the drawing for a temperature of approximately -l8 C., with iron and ultra-violet light as conjoint catalytic agent.

It is evident that our invention in its broadest aspects involves the liquid phase chlorination of propylene dichloride under conditions such that the direction of the entering chlorine atom is controlled so that the relative amounts of 1,1,2- trichlorpropane and 1,2,3-trichlorpropane isomers resulting are regulated within definite limits. The scope of our invention, therefore, is to be construed only in accordance with the appended claims, and it is not to be restricted to the particular temperatures, pressures, amounts of reactants or manipulative procedures described herein as merely illustrative of the novel process.

We claim:

1. A process for preparing chlorinated hydrocarbons which comprises reacting chlorine with propylene dichloride in the presence of metallic iron as a catalyst in the liquid phase under temperature conditions so selected that the relative proportions of the various products resulting in the reaction mixture are controlled.

2. A process for preparing an isomeric mixture comprising principally 1,1,2-trichlorpropane and 1,2,3-trichlorpropane, in which the relative proportions of the two isomers are controlled, which comprises reacting chlorine with propylene dichloride in the liquid phase in the presence of metallic iron as a catalyst, the temperature of chlorination being so selected that the relative percentages of the two isomers in the reaction product are controlled as desired.

3. A process which comprises reacting propylene dichloride in the liquid phase with chlorine in the presence of metallic iron as a catalyst, the temperature at which the chlorination is carried out being so selected from the temperature range, -20 C. to that temperature corresponding to the boiling point of propylene dichloride, that the relative amounts of 1,2,3-trichlorpropane and 1,1,2-trichlorpropane in the reaction mixture are controlled.

4. A process for preparing 1,1,2-trichlorpropane and 1,2,3-trichlorpropane so that the ratio of the amount of one isomer to that of the other in the glass tube extending com-' reaction product is controlled within definite limits, which comprises reacting propylene dichloride in the liquid phase with chlorine in the presence of metallic iron as a catalyst, the chlorination temperature being selected from those falling within the range, 20 C. to the boiling point of propylene dichloride, so that any desired ratio of the relative amounts of the two isomers in the reaction product results.

- 5. A process for preparing 1,1,2-trichlorpropane and 1,2,3-trichlorpropane from propylene dichloride under conditions such that the isomer 1,2,2-trichlorpropane is substantially absent which comprises reacting gaseous chlorine with propylene dichloride in the liquid phase at a temperature ranging from 20 C. to the boiling point of propylene dichloride and in the presence of metallic iron as a chlorination catalyst.

6. A process for preparing an isomeric mixture consisting predominately of 1,1,2-trichlorpropane and 1,2,3-trichlorpropane from propylene dichloride under temperature conditions such that the isomer 1,2,2-trichlorpropane is substantially completely absent which comprises reacting gaseous chlorine with propylene dichloride in the liquid phase at a temperature ranging from -20 C. to 97 C. and in the presence of a chlorination catalyst comprising metallic iron.

'7. In a process of chlorinating propylene dichloride in the liquid phase with chlorine in the l presence of metallic iron as a catalyst, the step which consists of so selecting the temperature of chlorination that the product consists predominately of 1,1,2-trichlorpropane and 1,2,3-trichlorpropane.

8. In a process of chlorinating propylene dichloride in the liquid phase with chlorine in the presence of metallic iron as a catalyst, the step which consists of so selecting the temperature of chlorination that the amount of 1,1,2-trichlorpropane in the reaction mixture bears any definite ratio desired to the amount of 1,2,3-trichlorpropane.

9. A process which comprises reacting propylene dichloride in the liquid phase with chlorine in the presence of metalliciron as a catalyst, said reactants being exposed to ultra violet light and the temperature at which the chlorination is carried out being so selected from the temperature range -20 C. to that temperature corresponding to the boiling point of propylene dichloride, that any desired ratio of 1,2,3-trichlorpropane to 1,1,2-trichlorpropane in the reaction mixture results.

10. A process for preparing 1,1,2-trich1orpr0- pane and 1,2,3-trichlorpropane so that the ratio of the amount of one isomer to that of the other in the reaction product is controlled within detinite limits, which comprises reacting propylene dichloride in the liquid phase with chlorine in the presence of metallic iron as a catalyst, said reactants being exposed to ultra violet light, the chlorination temperature being so selected from those falling within the range 20 C. to the boiling point of propylene dichloride that any desired ratio of the relative amounts of the two isomers in the reaction product results.

11. A process for preparing 1,1,2-trichlorpropane and 1,2,3-trichlorpropane from propylene dichloride under conditions such that the isomer 1,2,2 trichlorpropane is substantially absent which comprises reacting chlorine with propylene dichloride in the liquid phase at a temperature ranging from 20 C. to the boiling point of propylene dichloride, said reaction being carried out in the presence of metallic iron as a chlorination catalyst and said reactants being exposed to ultra violet light.

12. A process for preparing an isomeric mixture consisting predominately oi. 1,1,2-trichlorpropane and 1,2,3-trichlorpropane from propylene dichloride under conditions such that the isomer 1,2,2-trichlorpropane is substantially completely absent which comprises reacting chlorine with propylene dichloride in the liquid phase at a temperature ranging from 20 C. to 97 C., said reactants being exposed to ultra violet light and said reaction being carried out in the presence of metalliciron as a chlorination cata- 5 lyst.

ARTHUR A. LEVINE. OLIVER W. CASS. 

